The invention relates to a sheet feeder apparatus and more specifically to the structural arrangement of the suction pick-up heads for such a sheet feeder apparatus which are employed for lifting a sheet, for example a sheet of paper, from a stack. The pick-up heads are supported for a tilting movement in at least one direction, preferably in two directions, namely in the direction of feed advance and/or in the direction extending perpendicularly to the direction of feed advance whereby the respective tilting axes are arranged at right angles relative to each other.
Conventionally, the suction pick-up heads were supported on a cross rod in a tilting manner so that the pick-up nozzles with a picked up sheet secured thereto would perform an upward stroke slanted in the forward direction. In this manner, the leading edge of a picked up sheet, which is supposed to be aligned with a respective stop rail, is moved through a substantially linear upward movement whereby the sheet is to be picked up precisely as a basis for its precise feeding and before it is taken up by the conveyor suction heads.
German Pat. No. 1,098,012 discloses a feeder arrangement in which the pick-up heads are supported on a cross bar by means of support blocks, the angular position of which is adjustable relative to the longitudinal extension of the cross bar. The adjustment of the angular position of the suction heads in this prior art disclosure is possible only when the machine is not operating, because clamping screws must be released prior to the adjustment whereupon the clamping screws must be tightened again. The adjustment in the stationary position is possible about different tilting points or axes, for example, to tilt the respective suction head in the feed advance direction and in a direction extending perpendicularly thereto. The adjustment in the reference is intended to assure the proper stretching of the sheet material, especially flexible sheet material, during the pick-up movement and to avoid interference between the sheet being lifted and the sensing blowing means which sense the height of the stack.
German Pat. No. 832,896 discloses a sheet lifter apparatus in which the motion of the pick-up heads is controlled by cam and cam follower means. At least one member of these cam and cam follower means is adjustable by hand, even during the operation of the machine. However, this adjustment is not one which takes place automatically and continuously in responds to the particular operating condition prevailing at any one instant.
East German Pat. No. 80,719 discloses an apparatus for the adjustment of the suction heads during the operation of the machine for the purpose of varying the position where the suction head contacts the top sheet of a stack. For example, if the sheets have a line of perforations, for instance along the margin, the adjustment of the suction head is to avoid that they contact the sheet in the area of the perforation. To this end both suctions heads are adjusted simultaneously.
The disadvantage of adjusting the angular position of the suction heads during the time when the machine is not operated is seen in that it causes substantial down times during which the machine is not productive. Besides, repeated adjustments may be necessary in order to achieve the desired position of the suction heads suitable for a particular working condition or type of sheet material. Besides, the change of the material, for example, as to thickness and sheet size and the material quality will require readjustments and respective further down times of the machine.
Even the adjustment of the position of the suction heads by hand during the operation of the machine is not entirely satisfactory, since it does not provide an automatic adjustment, so that readjustments will be necessary from time to time, especially where the type, quality and/or size of the sheet material to be handled has been changed.